Combustion equipment for gas turbines with hot gas extraction and mixing means



April 15, 1958 F. M. JOHNSON EI'AL 2,830,439

COMBUSTION EQUIPMENT FOR GAS TURBINES WITH HOT GAS EXTRACTION AND MIXINGMEANS Filed Jan. 20, 1955 4 Sheets-Sheet 1 4 e 5 545 1o11 7s99 4B x c: aa l g mvmon B w M R 4 ATTORNEY? April 15, 1958 F. M. JOHNSON ETAL2,830,439

census-non EQUIPMENT FOR GAS TURBINES wnn HOT GAS EXTRACTION AND HIKINGMEANS Filed Jan. 20, 1955 v 4 Sheets-Sheet 2 J K i O I cl-- i; r 5 i 8 I3 g.

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I F ,5 E il l N 3 I 5 5 kW. ,ffir lT/ amon AT TORNEY S P 15, 1958 F. M.JOHNSON EIAL EQUIPMENT FOR GAS T 2,830,439 URBINES WITH HOT COMBUSTIONGAS EXTRACTION AND MIXING MEANS 4 Sheets-Sheet 3 Filed Jan. 20, 1955IIIIIIAIIIVIIIIIJIIII!IIIIII! VEN m J. 4 RHQM ATTORNEYS M BY April 15,1958 F. M. JOHNSON m; 2,830,439

COMBUSTION EQUIPMENT FOR GAS TURBINES IITH HOT GAS EXTRACTION AND MIXINGMEANS Filed Jan. 20; 1955 F l G 4 4 Sheets-She et 4 Inventors r 4. Aorneys 2,830,439 Patented Apr. 15, 1958 COMBUSTION EQUIPMENT FOR GAS AWITH HOT GAS EXTRACTION AND MIXING MEANS Francis Murray Johnson,Streatham, London, and Vernon Wallace Greenhough, Derby, England,assignors to Rolls-Royce Limited, Derby, England Application January 20,1955, Serial No. 483,082

Claims priority, application Great Britain February 24, 1954 9 Claims.(Cl. (ilk-39.74)

This invention relates tocombustion equipment and is particularlyapplicable to combustion equipment for gas turbine engines. I

Such combustion equipment normally comprises an air easing into whichair is delivered, and a flame tube within the air casing within whichcombustion'takes place. The combustion process is conveniently dividedinto a primary zone in which initial combustion of the fuel and airtakes place, and a secondary zone in which further air is added tocomplete the combustion process, and-in certain cases also further airis added to dilute the combustion products so as to reduce thetemperature of the gases at the exit from the combustion chamber.

According to this invention the combustion equipment comprises. aconduit which is led off from and returned, to the primary combustionzone of the flame tube, means including an ejector operated by a flow ofair supplied to the combustion equipment for creating a suflicientpressure difference at the ends of said conduit to'cause 9 in operationa flow of gas therethrough, and means to supply fuel to said conduit.

In using the word conduit there is implied apathway for a stream ofgas-which may in its course. be divided into different streams flowingin different passage-ways.

According to a feature of this invention thecombuation equipmentcomprises an outlet pipe connected to receive gases from theprimarycombustion zone at the,

flame tube, ejector means positioned at the outlet end of said pipe andsupplied with a flow of air so asto cause a region of low pressureadjacent the outlet end of .the pipe, a further pipe connected to saidregion of low pressure to receive said flow of air and the emerging fromthe outlet pipe and to convey them to within the primary zone of theflame tube, and means to supply fuel to said outlet pipe upstream ofits. outlet end to mix with the gases in the pipe.

According to a feature of the invention the means to supply fuel may bea fuel'atomiser.

According to one arrangement of the invention the flame tube is providedat its inlet end with an elongated tubular portion which opens at itsupstream end to the 5B. fixed to the casing. The compressor is driven bya.' j turbine 6 through a shaft 6A mounted bearings 68 I incoming airstream, and there is provided a second tube coaxially within the firsttube and having its upstream end downstream of the upstream end of theouter tube, a bellshaped baffle positioned coaxially within 'theupstreamend of the outer tube so as to provide between its outer surfaceand the inner surface of the outer tube a convergentpassage, thereby toproduce a low pressure region downstream of the lip of the baflle andadjacent the upstream end of the inner tube, and fuel injector meanspositioned within the inner tube so arranged that heated combustionproducts from the primary combustion zone enter the inner tube, havefuel injected to mix with them in flowing through that tube whereby thegases are cooled, and are caused to reverse in direction at the upstreamend of the inner tube to flow through the annular space across the entryduct to the air'casing. At the downstream end of the inner tube theremay be provided a perforated batile extending across the annular spacebetween the tube members and this baflie may form the support for theinner tube. The baffle may be formed integrally with the inner tube, andthe outer tubular portion may be formed as an integral part of theupstream end of the flame tube.

Examples of this invention are illustrated in the accompanying drawingsin which Figure 1 is a diagram of a gas turbine showing the combustionequipment. I

Figure 2 is a section through the upstream end of a tubular combinationchamber.

Figure 3 is a similar section through part of an annular combustionchamber.

Figure 4 is a cross-sectional view on a larger scale of the. fuelinjector-and's'urrounding tubes taken on line 4--4 of Figure 2 lookingin the direction of the arrows;

Figure 5 is a view similar to Figure 4 but taken on line 5-5 of Figure3.

Thegas turbine engineillustrated in Figure 1 consists of a casing 4 withan inlet 4A for air and an outlet 48 for. theiproducts of combustion.Air entering the inlet 4A entersthe "compressor comprising a rotor 5having a number of rotating bla'desj SA rotating between blades and-5C.

from-the compressor enters the air casing 10.01.v thecombustion:equipment and thence flows into the ""flame'tubes 11 in the mannerhereinafter described from whence itfpasses out through a series offixed turbine no'ule guide vanes 7 to drive the turbine.

The air entering the engine is guided over a cone 8 supported in acasing on members 8A and on leaving the turbine the gases pass over acone the casing bymembers 9A.

The combustion equipment is more particularly illustrated in Figure 2and comprises tubular air casings 10 and tubular flame tubes 11 withinthe air casings. The upstream portion 12 of each air casing is ofincreasing cross-section area and at its upstream end the air casing isformed with a flange 13 by which it is connected to a delivery duct 14of a compressor of the engine.

9 supported from The flame tube 11 at its upstream end 11A is also ofincreasing cross-section area in the direction of flow and it is formedwith an integral tubular upstream ex tension 15 which may projectinto'the compressor delivery duct. The extension is substantiallycylindrical in form, and thus there is formed an annular passage 16 ofsubstantially constant cross-section area between the upstream end'llaof the flame tube and its extension 15 and the wall of the delivery duct14 and the upstream part 12 of the air casing. The length of theextension 15-is about twice its diameter, and the extension is' formedat its upstream end with a lip 17 which is inclined slightly inward.

Coaxially within the extension of the flame tube there is mounted aninner tubular member 18 which is sub-- amount.

3 a,sso,sse stantially cylindrical man, being flaredslightly in theoutward direction at its end 1! remote fromthe upstream end of the flametube extension 15, and also being formed at end with aradially-extending perforatedweb which extends across the inner tubularmember 15 and the flame tube extension 15. The radially-extending web 2.is formed at its outer periphery with a flange 22 to lie within theflame tube 11 adjacent the point wherethe cylindrical extension 15 joinsthe increasing area part 11a of the flame tube, and

the web is secured to the flame tube as by welding or bolting: tosupport the inner tubular member ll within it.

The inner tubular member 18 is open at its other end 23, i. e., itsupstream end relative to the general direction of airflow, and coaxialwith this end 23 is provided a bell-shaped member 24, the lip of whichis of somewhat larger diameter than the.tubular member 18, thebell-shaped member 24 opening towards the open end of the tubular member18. The bell-shaped member 24 may axially overlap the tubular member 18so that the lip 25 surrounds the end 23 of the tubular member 18, asillustrated or the bell-shaped member 24 may terminate in the same planeas thetubular member 18, or the members may be axially spaced apart by asmall The lip 25 lies within the upstream end of the tubular extension15 of the flametube, and forms with the lip 17 a short annular passage26 which .is preferably convergent.

Webs 27 may be formed internally of the upstream end of the extension 15to position it concentrically over'thelip25ofthebell-shapedmember24,andthelatter may be formed internallywith webs 28 to position the tubular member 18 within it. t

The bell-shaped members24 are conveniently formed as part of theradially-extending struts 29 which .are

theannular passage 21 between 24, which thus acts as snejector. The flowthrough passage 26 causes a depression within the lip 25, thus promotinga vflow of hot gas from within the primary combustion area of the inletend 11a of the flame tube and through the inner tubular member 18towards the bell-shaped member 24. Fuel is injected into this gasthrough holes 33, which tends to cool the gas and thus to vaporizethe'fuel, and the mixture then reverses in direction to flow towards theinlet end 114 of the flame tube through the annular passage or pipe 21where intermi s l softhefuelandgaswiththeairentering through passage 26takes place.

Fuel, airand gas flow through the apertures in the web 22, the divergentshape of the inlet end of the flame tube and the flared end 19 of themember 18 causing the mixture to flow flrst away from the centre-line ofthe flame tube.

Part of the air flowing in passage 16 enters the flame tube throughinlets 36, 37 and is burned with the fuel entering through passage 21,the primary combustion taking place substantially within the inlet end11a of the flame tube; further air enters the downstream part of theflame tube, as is conventional, to provide for the completion ofcombustion and the dilution air.

InFigure3isasimilarviewtoFigure'2butahows the invention applied to anengine in which instead of a number of flame tubes annularly arranged,the flame tube 11 is" itself an annulus and has an annular outlet pipe18 leading otf from the primary combustion zone of the flame tube, anannular ejector member 24 and an annular extension 15 forming a pair ofreturn pasnormally provided between the inner and outer walls of thecompressor delivery duct 14, but may for example be formed as separateunits and secured say to the outer wall of the compressor delivery duct.Y

Within the inner tubular member 18 there is provided a fuel injector 30,which is preferably towards the end 1! of the inner member. The fuelinjector 3. may comprise a central body 31 and a number of shortclosedended pipes 32 extending radially of the body, the pipes beingformed with transverse drilled holes 33. The fuel injector is preferablysupported by a tubular member 34 extending through the open end 23 ofthe tubular member 18, and the tubular member 34 may be secured as shownto a boss 35 concentrically within the bell-shaped member 24. Where thelatter is formed as part ofja strut 29, fuel passages 38 will be formedin the strut leading from the fuel supply system of the engineto theinlet end of the tubular member 34, which'serves as the-fuel supply pipeto the fuel injector 30, and thence through passages in the injectorbody 31 and lhr l Plpes32 to the holes 33. These are preferably of smalldiameter to atomize the fuel. g

The inlet portion of the flame tube is also formed with furtherapertures for the admission of primary air which may be of anyconvenient form. For example, as shown, the inlet portion 11a of theflame tube is formed with a pair'of cylindrical tubular parts 36 atopposite sides of a diameter, and having their axes at their inlet endsparallel to the axis of the flame tube; The tubular parts 36 are ofsmall diameter relative to the'flame tube, and are turnedthroughapproximately a right angle so that their outlet ends 37 aredirected towards the centre-line of the flame tube and towards oneanother.

In operation, when air is delivered to the combustion equipment, themain part of the air flows through the annular passage 16, and a smallpart flows through the annular passage 26 between the lip 17 of thetubular eatension 15 and the lip 25 of the bell-shaped member 15 S.Combustion equipment for a gas-turbineenginehavsages or pipes 21. Anumber of fuel injectors 30 are spaced circumferentially within theoutlet pipe 18.

Like parts have like numbering to those shown in Figure 2. In additionthere is shown in Figure 3 a manifold 3! supplying fuelto the fuelintake bores 38 and a secondaryairinletstotheflame tube at4land41.

We claim:

1. Combustion equipment for a gas-turbine enginehavinganaircasingintowhichairisdeliveredandaflame tube within said aircasing and within which combustion takes place, the flame tube beingdivided into a primary zone into which air is delivered and in which combuation of the fuel takes place and a further zone into which furtherair is delivered comprising an elongated -conduit having its inlet endopen and connected to the primary combustion zone of the flame tube andits outlet end led back to said primary combustion zone, ejector meansoperated by the flow of air delivered into the flame tube and actingintermediate the length of said conduit to create a sufflcient pressurediflerenee between the ends of said conduit to cause in operation aflowof gas therethrough over the whole cross section thereof, and means,to supply fuel forcombustiontosaidconduitformovementbysaidflowtosaidprimaryaoneforinlflaleembmtion.

2. Combustion equipmentasclaimedincla'imlwh'ein said means to supplyfuel comprises a fuel atomizerconstructedtodirectfueljetstransverselytothedireetion of gas flow insaid conduit.

3. Combustion equipment as claimed in claim 1 wherein said conduitcomprises an outlet pipe connected, to receivegasesfrom the primarycombustionsoneoftheflame tubeand areturnpipetoleadsaidgasesbacktotheprlmary none, ejector means positioned at the outletend ofthe outlet pipe and operated by saidflow of air to cause a regionof low pressure adjacent the outlet end of said out-- let pipe, saidflow of air passing into said return pipe together with gases from theoutlet pipe, and means to supply fuel into said outlet pipe upstream ofits outlet end to mix with the gases in; the pipe.

4. Combustion'equipment as claimed in claim 3 wherein said means tosupply fuel comprises a fuel atomizer.

, ing its inlet end opening to within the flame ing an air easing intowhich air is delivered and a flame tube within said air casing andwithin which combustion takes place, the flame tube being divided into aprimary zone into which air is delivered and in which initial combustionof the fuel takes place and a further zone into which further air is atits inlet end an elongated tubular portion which opens at its upstreamend to the flow of air being delivered into the air casing, andcomprising an inner tubular member co-axially within the elongatedtubular portion and having its outlet end on the side of the upstreamend of the elongated portion toward said primary zone, a bell-shapedbaflie positioned co-axially within the upstream end of the elongatedtubular portion and having a lip adjacent the outlet end of the innertubular member, thereby to define between its outer surface and theinner surface of the elongated tubular portion a convergent passage andto produce a low-pressure region downstream of its lip, and fuel mjectormeans positioned within the inner tubular member upstream of its outletend.

6. Combustion equipment as claimed in claim 5, comprising also means tointroduce mary combustion zone in addition to that entering through saidelongated tubular portion of the flame tube.

7. Combustion equipment as claimed in claim wherein there are providedradially-extending struts immediately upstream of the flame tube, andwherein said bellshaped bame and from said struts.

8. Combustion equipment for a gas-turbine engine having a easing intowhich air is delivered and a flame tube within said casing, the flametube having a primary tube and havdelivered, wherein the flame tube hasfurther air into the prisaid fuel injector means are supported at itsupstream end to the air flowing in said casing, an

inner tubular member within the tubular portion and having its inlet endopen adjacent the primary zoneof theflame tube and having its outlet endopen near the upstream end of the elongated tubular portion, a turningbatfle positioned to divert the gas flow from the outlet end of theinner tubular member into the inlet end of the'elongated tubularportion, said bafile being spaced from the walls of the last mentionedportion to define a convergent passage for the air from the casing toproduce a low pressure region adjacent the outlet end of the innertubular member, and fuel injector means positioned within the innertubular member upstream of its outlet end.

9. The combustion equipment as defined in claim 8 in which flame tubehas a rapidly enlarging section adjacent the elongated tubular portion,and means extending through said section adapted to direct air from thecasing radially inwardly toward the center of the said primary zone ofthe flame tube.

References Cited in the file of this patent UNITED STATES PATENTS GreatBritain Feb. 24, 1954

